Terminal blocks typically comprise a block of insulation bearing a series of circuit connecting devices. A terminal block may consist of a row of separate modular units, or a single unitary structure may be used. The terms "terminal block" and "a support of insulation" as used herein refer to both forms of construction.
The connecting devices of a terminal block connect a first series of wires to a corresponding second series of wires, each connecting device and the wires it interconnects being called "a circuit". It is common to label the circuits, as an aid to technicians in connecting the wires initially and in providing service subsequently.
Circuit-identifying labels are sometimes adhered to the inside of a hinged door or panel which, when in its "open" position, provides circuit-identifying marks aligned with respective wiring terminals. With the door open, the labels are positioned to one side of the terminals. For more direct identification of the circuits it is common to mount marking strips directly on the terminal blocks. In one form, the marking strip is applied along an area of a terminal block between two rows of wire fasteners. It may be necessary to make the terminal block wider than it would ordinarily be in order to provide space for the marking strip. More compact terminal blocks that do not have a free space for mounting a terminal strip can still be marked, by providing a special form of marking strip that is applied to the terminal block over an area where screws of the connecting devices are distributed. The marking strip has punched holes for access to the screws. The areas of the marking strip between the holes is used for circuit-identifying characters.